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  • Final Activity Report Summary - SUSTREPRO (The development and evaluation of natural and sustainable methods for the regulation of fertility in production systems for small ruminants)

Final Activity Report Summary - SUSTREPRO (The development and evaluation of natural and sustainable methods for the regulation of fertility in production systems for small ruminants)

The principle objective of the research program was to develop hormone free methods of controlling reproduction in small ruminants through natural manipulation of three environmental factors know to affect reproduction in small ruminants these are nutrition, photoperiod and socio-sexual signals. Three research projects have been completed. The first project was a study of the effect of nutrition on seasonality of reproduction in sheep. The results show that undernutrition modified the photoperiod-driven expression of reproductive seasonality and that in the spring, reproductive activity stopped sooner in under nourished ewes that was associated with a reduction in circulating melatonin. Although the early results suggested that undernutrition altered the circadian clock that entrained the rhythm of melatonin this was confirmed by later studies. It now appears that undernutrition has effects on the amplitude of melatonin secretion that alters the secretion of GnRH.

The results of parallel studies have shown that the energy sensing AMPK (adenosine mono phosphate kinase) system is implicated in this mechanism. Complimentary studies examining the site of the interaction between photoperiodic influences on reproduction suggest that the interaction occurs at the level of the GnRH pulse generating system. A second project examined the interaction between nutrition and socio-sexual signals that affect reproduction. The main socio-sexual signal affecting reproduction in small ruminants is the "male effect", where by the introduction of a male into a group of females that are anoestrus (that is females that are not reproductively active) can stimulate reproductive activity in a high proportion of stimulated females.

The first experiments described the effects of nutrition and genotype on the response to the male effect. From these studies a number of important scientific issues became apparent and so we addressed these. First, our studies revealed that the ovary was an important, source of variability and highlights a critical need to examine the physiology of folliculogenesis in anoestrus and studies in this subject are now commencing at INRA.

Secondly, studies with goats have shown an interaction between nutrition and the "male effect" but, using sheep in France we were unable to confirm this. Complimentary basic investigations into the follicular physiology of anoestrous ewes and its relationship to the ram effect have shown that short cycles are not caused by the premature secretion of uterine prostaglandin F2? and that they are associated with a suppression of progesterone synthesis associated with reduced gene expression of some essential components of the biosynthetic pathway for progesterone (e.g. StAR and 3?HSD).

The project examined the effect of nutrition on folliculogenesis. In sheep, short-term nutritional supplementation stimulates folliculogenesis and understanding how is critical to the development the feeding systems required to develop hormone free manipulation of reproduction. These experiments have been carried out using sheep. In France, research examined the intra-ovarian insulin-glucose system while complimentary experiments in Tunisia examined how nutrition stimulated this insulin-glucose system.

The results show that nutrition reduced the intra follicular concentration of aromatase in the granulosa without any change in the level of FSH and it was associated with a reduction in the secretion of follicular oestradiol but an increase in the number of follicles. Furthermore, these findings could be replicated by the infusion of glucose. These results demonstrate that the effect of nutritional supplementation on folliculogenesis is at the level of the follicle. Further analysis of samples from both these experiments have shown that both nutritional supplementation and infusion of glucose induced changes in follicular physiology that were associated with changes in the intra-follicular insulin signalling.

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